I was not able to reproduce the case where tooltips are shown. Could you please make sure that there is no other place where this is set to true. If not are you able to reproduce it in a blank new project?
Here is how to get the drop-down list:
sender, EventArgs e)
var listElement = sender
var dropDown = listElement.ElementTree.Control
var ddl = dropDown.OwnerDropDownListElement;
I hope this will be useful. Let me know if you have additional questions.